An in-vehicle navigation device for displaying a map around a current position of a vehicle, for calculating an optimum route to a destination and for guiding the route based on a map data includes a hard disk drive (i.e., HDD). The HDD as a memory stores the map data and the like.
The HDD is a memory device for reading and writing a data in a disk by using a magnetic head. The disk is a memory medium, on which magnetic material is applied. When the HDD functions, the magnetic head floats from the disk by a small clearance between the head and the disk with air pressure generated by rotation of the disk because of air viscosity. The magnetic head is disposed over the disk.
Accordingly, when the HDD functions under a condition where atmospheric pressure around the vehicle is very low, the air pressure for floating the magnetic head is reduced. Thus, the clearance between the head and the disk may not be sufficient. As a result, the head may collide with the disk, so that the disk is damaged.
Thus, when the in-vehicle navigation device includes the HDD, a certain countermeasure technique is required for protecting the HDD from being damaged in a case where the device may be used at a high altitude place having an altitude equal to or larger than a predetermined altitude, at which the function of the HDD is guaranteed. For example, the predetermined altitude is 3000 meters high, 4000 meters high or 5000 meters high.
When the vehicle reaches the predetermined altitude, for example, 3000 meters high, a part of the map data stored in the HDD is transferred to and stored in an external memory. Then, the HDD stops functioning. Thus, while the vehicle drives in a high altitude area, the navigation device guides the route based on the map data stored in the external memory. This is disclosed in, for example, JP-A-2004-317385, which corresponds to U.S. Pat. No. 7,171,305. Therefore, the HDD stops operating when the vehicle is disposed in the high altitude area, so that the disk is prevented from being damaged although the navigation device continues to guide the route.
However, in an in-vehicle navigation device, the device has not only route guiding function but also other functions. If the data corresponding to the other functions is stored in the HDD, the other functions are not available when the vehicle is disposed in the high altitude area.
For example, the navigation device may rip a song in a compact disk (i.e., CD) on the HDD, and/or download information from the Internet so that audio data is stored in the HDD. Thus, the navigation device plays the song and/or the audio data.
The above navigation device cannot play the audio data and/or the song stored in the HDD when the HDD stops functioning in a case where the vehicle is disposed in the high altitude area.
In this case, even if the audio data is transferred to the external memory, and the HDD continues to output the audio data because the device plays the audio data, the HDD stops functioning when the vehicle enters into the high altitude place. In this case, the playing of the song is interrupted. Thus, a user may feel discomfort. On the other hand, when the HDD stops functioning after the playing of the song ends, the disk may be damaged while the device plays the song since the HDD functions in the high altitude place, which is equal to or higher than the predetermined altitude.
Thus, it is required for an audio system to stop functioning the HDD without giving discomfort to the user even when the HDD stops functioning while the audio system plays the audio data in the HDD.